In McGregor et al, U.S. Pat. No. 2,398,187, incorporated herein by reference, there are disclosed compositions for use as dampening fluids in hydraulic machinery, such as shock absorbers, artillery recoil mechanisms, door checks, railroad car couplings, aircraft landing struts, and the like. These fluids comprise mainly silicone fluids, with the remainder of any liquid medium being an organic lubricant.
Almost all conventional shock absorber assemblies are based on the same principle, i.e., using an assembly comprising a movable member within an enclosing chamber and including at least one rubber seal means, the assembly being filled with a quantity of a hydraulic fluid composition for dampening. All such systems have certain disadvantages, one being that a fluid must be provided which does not lead to any substantial swelling of the rubber seal (See McGregor et al, for example).
Other disadvantages of damper systems which employ a fluid dampening medium are described in Kendall, U.S. Pat. No. 3,053,526, incorporated herein by reference. For instance, such fluid systems require exact machine tooling and high pressure seals to prevent leakage of the fluid. Also, while a fluid medium provides viscous damping and exponential velocity damping, it does not provide any significant friction damping.
Kendall indicates that if a compressible solid is used in a standard damper, instead of liquids or other fluids, it is possible to achieve various types of damping and other advantages which are not available from the use of liquids. For example, with the use of compressible solids, friction damping, as well as viscous and exponential velocity damping, can be obtained from the action of the solid on the movable damper piston. Moreover, Kendall indicates that when compressible solids are used there is no need for the exact machine tooling and high pressure seals required to overcome the leakage problems which a fluid medium presents.
It has been found that if the solid material is highly compressible, it is more useful as a damper because the greater the compressibility, the greater the ability of the compound to absorb energy and to return the movable piston to its original starting point. Silicone compounds are not only highly compressible, but possess the necessary wide temperature range stability which is required. Solid silicone rubber compounds of the prior art, however, contain fillers for reinforcement, such as silicas and ferric oxides, and these are relatively incompressible.
Applicants have now discovered a more compressible and more readily usable solid damper composition for an energy-absorbing assembly. Unlike conventional compositions applicants' invention is a one-part system which does not require mixing prior to curing. Moreover, applicants' system obviates the need for fillers. Thus a composition is provided which affords economic advantages and greater efficiency as compared to prior solid damper compositions. Applicants have also discovered that if the solid silicone mass is fragmented, it provides greater energy dissipating ability when impact is imparted to the damper assembly.
Such advantages lend themselves to important utility in heavy duty shock absorbing devices and particularly to heavy motive machinery shock damping and safety devices. A particularly important field of use is in automotive shock absorbers and especially automotive safety bumpers.